Switch out Gruyere cheese for WHAT in a Potato-Leek Gratin recipe?

I used this amazing recipe last Christmas for a gratin but I hate Gruyere cheese, and anything that evenly remotely tastes like Swiss. I mistakenly used cheddar instead without realizing that it's a much saltier cheese and totally ruined it! I want to make it again, but need other cheese options that are less salty and less "Swiss-y!" Thank you so much!

Queso Quesadilla a Mexican melting cheese widely available and affordable.
Although, it might have a bit of the salty taste but far less sharp than Swiss.
I find supermarket Mozzarella a bit bland, plastic like, use the Queso Quesadilla for pizza when I can't get good mozzarella.

is emmenthal too swiss-y? i agree with trying parmesan. it might not turn out as gooey-cheesy, but i think the flavor would be great. there's also a younger version of asiago called asiago pressato that is mild but also has the melty-gooey quality. it's my favorite (along with gruyère) in a grilled cheese sandwich.

I'd say parm, but if you don't like pungent and salty, you might be more apt to try provolone, a great melting, relatively mild cheese. Or, for even more mild, mozzarella. I almost want to say you can do a goat cheese if you're a fan, but I'm trying to imange the goat cheese with leeks, and I'm not so sure I'm feeling that.